U.S. patent application number 10/443549 was filed with the patent office on 2004-11-25 for acoustic beam forming in phased arrays including large numbers of transducer elements.
This patent application is currently assigned to Insightec-Image Guided Treatment Ltd.. Invention is credited to Ezion, Avner, Vitek, Shuki, Vortman, Kobi.
Application Number | 20040236253 10/443549 |
Document ID | / |
Family ID | 33450444 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040236253 |
Kind Code |
A1 |
Vortman, Kobi ; et
al. |
November 25, 2004 |
Acoustic beam forming in phased arrays including large numbers of
transducer elements
Abstract
A focused ultrasound system includes a transducer array, a
controller for providing drive signals to the transducer array, and
a switch. The transducer array includes a plurality of "n"
transducer elements, and the controller includes a plurality of "m"
output channels providing sets of drive signals having respective
phase shift values, "m" being less than "n." The switch is coupled
to the output channels of the controller and to the transducer
elements, and is configured for connecting the output channels to
respective transducer elements. The controller may assign the
transducer elements to respective output channels based upon a size
and/or shape of a desired focal zone within the target region, to
steer or otherwise move a location of the focal zone, and/or to
compensate for tissue aberrations caused by tissue between the
transducer array and the focal zone, geometric tolerances and/or
impedance variations of the transducer elements.
Inventors: |
Vortman, Kobi; (Haifa,
IL) ; Vitek, Shuki; (Haifa, IL) ; Ezion,
Avner; (Haifa, IL) |
Correspondence
Address: |
Bingham McCutchen LLP
Suite 1800
Three Embarcadero Center
San Francisco
CA
94111-4067
US
|
Assignee: |
Insightec-Image Guided Treatment
Ltd.
Tirat Carmel
IL
|
Family ID: |
33450444 |
Appl. No.: |
10/443549 |
Filed: |
May 22, 2003 |
Current U.S.
Class: |
601/2 |
Current CPC
Class: |
A61N 2007/0065 20130101;
G10K 11/346 20130101; A61N 2007/0095 20130101; A61N 7/02 20130101;
A61N 2007/0078 20130101; A61N 2007/0091 20130101 |
Class at
Publication: |
601/002 |
International
Class: |
A61N 007/00 |
Claims
What is claimed:
1. A system for focusing acoustic energy towards a target region,
comprising: a transducer array comprising a plurality of "n"
transducer elements; a controller for providing drive signals to
the transducer array, the controller comprising a plurality of "m"
output channels providing sets of drive signals having respective
phase shift values, "m" being less than "n;" and a switch coupled
to the output channels of the controller and to the transducer
elements of the transducer array, the switch configured for
connecting output channels to respective transducer elements in
order to provide respective sets of drive signals to the respective
transducer elements, whereby acoustic energy transmitted by the
transducer array may be focused in a desired manner.
2. The system of claim 1, wherein the switch comprises a
cross-point matrix or a multistage interconnection network
(MIN).
3. The system of claim 1, wherein the switch comprises a plurality
of "m" inputs coupled to the output channels of the controller, a
plurality of "n" outputs coupled to the transducer elements, and a
plurality of switching elements for connecting each of the inputs
to one or more of the outputs.
4. The system of claim 1, wherein the switch is configured for
coupling each output channel to more than one of the transducer
elements.
5. The system of claim 1, wherein the controller is configured for
assigning phase shift values to each of the transducer elements at
least partially based upon an analysis of an acoustic path
extending from each of the transducer elements to a desired focal
zone within the target region.
6. The system of claim 5, further comprising an imaging apparatus
for performing the acoustic path analysis, the controller coupled
to the imaging apparatus for obtaining data related to the acoustic
path analysis from the imaging apparatus.
7. The system of claim 1, wherein the controller is coupled to the
switch for configuring the switch in order to connect the output
channels to the respective transducer elements.
8. The system of claim 1, wherein the controller is configured for
assigning each of the transducer elements to a respective output
channel based upon one or more parameters related to a course of
treatment of a target tissue region using the transducer array.
9. The system of claim 8, wherein the controller is configured for
assigning the transducer elements to respective output channels
based upon at least one of a size of a focal zone within the target
region into which the acoustic energy from the transducer array is
focused, a shape of the focal zone, a location of the focal zone,
tissue aberrations caused by tissue between the transducer array
and the focal zone, geometric tolerances of the transducer array,
and impedance variations between the transducer elements.
10. The system of claim 1, wherein the controller is configured for
focusing the acoustic energy from the transducer array during a
series of sonications into a target region, the switch being
configurable before each sonication for focusing the acoustic
energy into the target region to treat tissue within the target
region.
11. The system of claim 1, wherein controller is configured for
assigning the transducer elements to respective output channels via
the switch in order to steer a focal zone within the target region
in a desired manner.
12. A transducer array for delivering acoustic energy to a target
region, comprising: a plurality of "n" transducer elements arranged
on a substrate; and a switch coupled to the transducer elements and
comprising a plurality of "m" input channels and "n" output
channels coupled to the transducer elements, "m" being less than
"n," each input channel being connectable to a controller for
receiving drive signals comprising respective phase shift values,
the switch configured to couple the input channels to respective
transducer elements in order to provide drive signals to the
respective transducer elements, whereby acoustic energy transmitted
by the transducer elements may be focused in a desired manner.
13. The transducer array of claim 12, wherein the switch is mounted
to the substrate using flexible interconnects having no significant
impact on acoustic properties of the transducer elements.
14. A method for delivering acoustic energy from a transducer array
comprising a plurality of "n" transducer elements, the method
comprising: assigning one of "m" phase shift values to each of the
transducer elements, "m" being less than "n;" and delivering "m"
sets of drive signals to the transducer array, each set of drive
signals comprising a respective phase shift value selected from the
"m" phase shift values; connecting the sets of drive signals to
respective transducer elements based upon the phase shift values
assigned to the respective transducer elements, whereby acoustic
energy transmitted by the transducer elements may be focused in a
desired manner towards a target region.
15. The method of claim 14, wherein connections between the sets of
drive signals and respective transducer elements are reconfigured
dynamically while acoustic energy is transmitted by the transducer
elements.
16. The method of claim 14, wherein the phase shift values are
assigned to the transducer elements at least partially by analyzing
an acoustic path from each of the transducer elements to the target
region, and assigning a phase shift value to each of the transducer
elements based upon the acoustic path analysis.
17. The method of claim 16, wherein the phase shift value assigned
to each of the transducer elements is compared to phase shift
values of the sets of drive signals, and wherein each transducer
element is assigned to a set of drive signals that has a phase
shift value that approximates the phase shift value assigned to the
respective transducer element.
18. The method of claim 16, wherein a table is generated during the
acoustic path analysis that identifies the sets of drive signals
assigned to each of the transducer elements, and wherein the table
is used at least partially to configure a switch coupled to the
transducer elements to connect the transducer elements to
respective sets of drive signals.
19. The method of claim 14, wherein the transducer array is
disposed adjacent to a body, and wherein the transducer elements
transmit acoustic energy into the body towards a focal zone within
the target region when connected to the sets of drive signals.
20. The method of claim 19, wherein the acoustic energy is
transmitted for sufficient time to ablate tissue within the target
region.
21. The method of claim 19, wherein the phase shift values are
assigned to the transducer elements at least partially to steer the
focal zone within the target region relative to a central axis of
the transducer array.
22. The method of claim 19, wherein the phase shift values are
assigned to the transducer elements in order to focus the acoustic
energy at multiple focal zones within the target tissue region.
23. A method for delivering acoustic energy from a transducer array
comprising a plurality of "n" transducer elements to a target
region, the method comprising: providing "m" sets of drive signals,
each set of drive signals comprising a respective phase shift value
selected from "m" phase shift values, "m" being less than "n;"
connecting a first set of the drive signals to a first plurality of
the transducer elements; and connecting a second set of the drive
signals to a second plurality of the transducer elements, whereby
acoustic energy is transmitted by the first and second plurality of
transducer elements and focused in a desired manner into the target
region.
24. The method of claim 23, wherein each of the "m" sets of drive
signals is connected to a plurality of the "n" transducer elements,
whereby each of the transducer elements is connected to one of the
sets of drive signals.
25. The method of claim 24, further comprising: analyzing an
acoustic path from each of the transducer elements to the target
region; determining a phase shift value for each of the transducer
elements based upon the acoustic path analysis; connecting each of
the transducer elements to one of the sets of drive signals at
least partially based upon the phase shift values of the respective
transducer elements and the sets of drive signals.
26. The method of claim 25, wherein desired phase shift values are
assigned to each of the transducer elements based upon at least one
of a size, shape, and location of a focal zone within the target
region, and wherein the desired phase shift values are combined
with the phase shift values determined based upon the acoustic path
analysis.
27. The method of claim 26, wherein the combined phase shift values
for the transducer elements are compared to the phase shift values
of the sets of drive signals, and wherein the transducer elements
are assigned to respective sets of drive signals having phase shift
values that approximate the combined phase shift values of the
respective transducer elements.
28. The method of claim 23, the first and second plurality of
transducer elements are connected to first and second sets of drive
signals based upon at least one of a size, shape, and location of a
focal zone within the target region.
29. The method of claim 22, wherein the acoustic energy transmitted
by the first plurality of transducer elements is focused at a
different location within the target region than the acoustic
energy transmitted by the second plurality of transducer elements.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to systems and
methods for delivering acoustic energy into a body, and more
particularly to systems and methods for focusing acoustic energy
transmitted from a transducer array including a large number of
transducer elements.
BACKGROUND
[0002] Focused ultrasound systems have been suggested for
delivering acoustic energy into a tissue region within a patient,
such as a cancerous or benign tumor, to coagulate or otherwise
treat the tissue region with thermal energy. For example, a
piezoelectric transducer located outside the patient's body may be
used to focus high intensity acoustic waves, such as ultrasonic
waves (acoustic waves with a frequency greater than about twenty
kilohertz (20 kHz)), at an internal tissue region of a patient to
treat the tissue region. The acoustic waves may be used to ablate a
tumor, thereby eliminating the need for invasive surgery. Such an
acoustic transducer system is disclosed in U.S. Pat. No. 4,865,042
issued to Umemura et al.
[0003] When delivering acoustic energy, it is useful to control the
shape of a "focal zone" (the volume of tissue treated when the
acoustic energy is focused into a tissue region), to control "focal
depth" (the distance from the transducer to the focal zone), and/or
to correct for tissue aberrations that may be caused by intervening
tissue between the transducer and the tissue region. It is also
desirable to steer the acoustic energy away from a central axis of
the transducer, e.g., at large steering angles relative to the
central axis.
[0004] To facilitate steering acoustic energy, it is desirable to
make the transducer elements as small as possible, preferably on
the order of the wavelength of the acoustic energy transmitted by
the transducer elements. For example, for acoustic energy having a
frequency of one Megahertz (1 MHz), it would be desirable to
provide transducer elements having a width or other maximum
cross-section of less than one millimeter (1.0 mm). For a
relatively large area transducer array, the total number of such
transducer elements required would become very large, i.e.,
requiring hundreds or even thousands of transducer elements.
[0005] The problem with providing so many transducer elements is
that individual sets of drive signals must be delivered to each
transducer element in order for the transducer elements to transmit
acoustic energy. Thus, hundreds or thousands of wires or cables
would be required to deliver the drive signals to the transducer
elements. The resulting system would be complicated and expensive
to implement.
[0006] Accordingly, systems and methods for delivering acoustic
energy from transducer arrays including many transducer elements
would be useful.
SUMMARY OF THE INVENTION
[0007] The present invention is directed to systems and methods for
delivering acoustic energy from a transducer array, and more
particularly to systems and methods for focusing and/or steering
acoustic energy from a transducer array including a large number of
transducer elements, preferably into a body of a patient for
ablating or otherwise treating tissue with the patient's body.
[0008] In accordance with one aspect of the present invention, a
system is provided for focusing acoustic energy towards a target
region that includes a transducer array, a controller for providing
drive signals to the transducer array, and a switch. The transducer
array may include a plurality of "n" transducer elements, and the
controller may include a plurality of "m" output channels providing
sets of drive signals having respective phase shift values, "m"
being less than "n."
[0009] The switch, e.g., a cross-point matrix or a multistage
interconnection network ("MIN"), may be coupled to the output
channels of the controller and to the transducer elements. The
switch may be configured for connecting output channels to
respective transducer elements in order to provide respective sets
of drive signals to the respective transducer elements, whereby
acoustic energy transmitted by the transducer array may be focused
in a desired manner. In one embodiment, the controller may be
coupled to the switch for configuring the switch in order to
connect the output channels to the respective transducer
elements.
[0010] Using a switch with "m" drive channels to control drive
signals provided to a relatively large number of "n" transducer
elements may substantially minimize the complexity of the system,
since relatively few drive channels may be needed for a relatively
large number of transducer elements. It may also allow complex
phase patterns to be created in a sub-set of transducer elements or
using the entire transducer array, while using a limited number of
input drive channels. In addition, because a limited number of
drive channels deliver power to a relatively large number of
transducer elements, the drive channels may be loaded substantially
evenly, as desired for statistically even phase distribution.
[0011] The controller may be configured for assigning each of the
transducer elements to a respective output channel based upon one
or more parameters related to a course of treatment of a target
tissue region using the transducer array. For example, the
controller may assign the transducer elements to respective output
channels based upon a size of a focal zone within the target
region, a shape of the focal zone, axial and/or angular location of
the focal zone, impedances of the transducer elements, and/or
tissue aberrations caused by tissue between the transducer array
and the focal zone.
[0012] In accordance with another aspect of the present invention,
a transducer array is provided for delivering acoustic energy to a
target region that includes a plurality of "n" transducer elements
arranged on one or more substrates, and a switch coupled to the
transducer elements. The switch may be coupled to the substrate(s),
e.g., via electrical connections that are flexible enough not to
impact substantially the acoustic characteristics of the transducer
array.
[0013] The switch may include a plurality of "m" input channels and
"n" output channels coupled to the transducer elements, "m" being
less than "n." Each input channel of the switch may be connectable
to a controller for transferring only selected drive signals
including respective phase shift values, the switch configured to
couple the input channels to respective transducer elements in
order to provide drive signals to the respective transducer
elements, whereby acoustic energy transmitted by the transducer
elements may be focused in a desired manner.
[0014] In one embodiment, the transducer array may include a single
substrate, and the switch may be mounted to the substrate.
Alternatively, the transducer array may include a plurality of
substrates that may be fixed or adjustable physically relative to
one another. Each substrate may include "n.sub.i" transducer
elements, which may be selectively connected to a subset of the "m"
input channels, "m.sub.k," or to all of the "m" input channels,
where the total number of all transducer elements is "n"
(.SIGMA.n.sub.i=n).
[0015] In accordance with yet another aspect of the present
invention, a method is provided for delivering acoustic energy from
a transducer array comprising a plurality of "n" transducer
elements. One of "m" phase shift values may be assigned to each of
the transducer elements, "m" being less than "n." For example, the
phase shift values may be assigned to the transducer elements to
steer the focal zone within the target region relative to a central
axis of the transducer array. In addition, or alternatively, the
phase shift values may be assigned to the transducer elements in
order to focus and/or steer the acoustic energy at multiple focal
zones within the target tissue region.
[0016] The "m" sets of drive signals may be delivered to the
transducer array, each set of drive signals including a respective
phase shift value selected from the "m" phase shift values. The
sets of drive signals may be connected to respective transducer
elements based upon the phase shift values assigned to the
respective transducer elements, whereby acoustic energy transmitted
by the transducer elements may be focused in a desired manner
towards a target region. For example, the transducer array may be
disposed adjacent to a patient's body, and the acoustic energy may
be transmitted into the body towards a focal zone within the target
region, e.g., for sufficient time to ablate tissue within the
target region. Optionally, the configuration of the switch may be
reconfigured dynamically during a procedure, e.g., to move the
focal zone and/or compensate for parameters encountered during the
procedure.
[0017] In accordance with still another aspect of the present
invention, a method is provided for delivering acoustic energy from
a transducer array including a plurality of "n" transducer elements
to a target region. "M" sets of drive signals may be provided, each
set of drive signals including a respective phase shift value
selected from "m" phase shift values, "m" being less than "n." A
first set of the drive signals may be connected to a first
plurality of the transducer elements, and a second set of the drive
signals may be connected to a second plurality of the transducer
elements, whereby acoustic energy is transmitted by the first and
second plurality of transducer elements and focused in a desired
manner into the target region.
[0018] Preferably, each of the "m" sets of drive signals is
connected to a plurality of the "n" transducer elements, whereby
each of the transducer elements is connected to one of the sets of
drive signals. Each of the transducer elements may be connected to
one of the sets of drive signals at least partially based upon
phase shift values assigned to the transducer elements based upon
at least one of a size, shape, and/or location of a focal zone
within the target region, to compensate for tissue aberrations that
may occur along an acoustic path from each of the transducer
elements to the focal zone, to set equal power distribution between
drive channels, and/or to compensate for impedance variations
between the transducer elements.
[0019] Other objects and features of the present invention will
become apparent from consideration of the following description
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Preferred embodiments of the present invention are
illustrated by way of example, and not by way of limitation, in the
figures of the accompanying drawings, in which like reference
numerals refer to like components, and in which:
[0021] FIG. 1 is a schematic diagram of a focused ultrasound
system, in accordance with the present invention.
[0022] FIG. 2 is a schematic side view of a patient on a
water-filled table being treated using a focused ultrasound system,
such as that shown in FIG. 1.
[0023] FIGS. 3A-3C are exemplary tables, showing desired phase
shift values for transducer elements of a transducer array,
associating the desired phase shift values with phase shift values
assigned to output channels of a driver, and a switch configuration
for connecting the transducer elements to respective output
channels, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] Turning now to the drawings, FIGS. 1 and 2 depict an
exemplary embodiment of a focused ultrasound system 10, including a
transducer array 14, a driver 16, a controller 18, and a switch 20,
in accordance with the present invention. As best seen in FIG. 2,
the transducer array 14 may deliver acoustic energy represented by
acoustic beam 15 into a target region 92, e.g., a benign or
malignant tumor or other tissue volume, within a patient's body 90,
to ablate or otherwise treat tissue within the target region 92. As
explained further below, the switch 20 connects the transducer
array 14 to the driver 16 and/or to the controller 18 in order to
steer and/or focus the acoustic energy transmitted by the
transducer array 14 in a desired manner.
[0025] With particular reference to FIG. 1, the transducer array 14
generally includes multiple transducer elements 22 arranged in a
pattern on a substrate 24. The substrate 24 may be a frame, a
planar or curved structure, and the like, onto which the transducer
elements 22 may be mounted or otherwise provided. In one
embodiment, the transducer array 14 may have a concave or bowl
shape, such as a "spherical cap" shape, i.e., having a
substantially constant radius of curvature such that the transducer
array 14 has an inside surface defining a portion of a sphere,
although alternatively, the substrate 24 may define a non-spherical
surface. For example, the transducer array 14 may have an outer
diameter between about eight and sixteen centimeters (8-16 cm), and
a radius of curvature between about eight and twenty centimeters
(8-20 cm). Alternatively, the transducer array 14 may have a
substantially flat configuration (not shown), may include an outer
perimeter that is generally circular, and/or may have a square,
linear, hexagonal or other symmetrical or asymmetrical shape (not
shown).
[0026] The transducer array 14 may be divided into any desired
number "n" of transducer elements 22.sub.1, 22.sub.2 22.sub.3, . .
. 22.sub.n, as seen in FIG. 1, and/or into a plurality of subsets
of transducer elements, each with a plurality of transducer
elements. For example, the transducer array 14 may be divided into
concentric rings and/or circumferential sectors to provide the
transducer elements 22. In one embodiment, the transducer array 14
may include between ten and forty (10-40) rings and between four
and sixteen (4-16) sectors. In alternative embodiments, the
transducer 14 may include transducer elements 22 having a variety
of geometric shapes, such as hexagons, triangles, circles, squares,
and the like (not shown).
[0027] The transducer elements 22 may be disposed about a central
axis "z," preferably but not necessarily, in a substantially
uniform or symmetrical configuration. Preferably, although not
necessarily, the transducer elements 22 have substantially the same
surface area as one another and/or may have similar or different
sizes and shapes than one another. Additional information on the
construction of transducer arrays appropriate for use with the
present invention may be found, for example, in co-pending
application Serial No. 09/884,206, filed Jun. 19, 2000. The
disclosures of this application and any references cited therein
are expressly incorporated herein by reference.
[0028] A transducer array 14 in accordance with the present
invention may include many transducer elements, e.g., hundreds or
thousands of transducer elements built as a single dish, or as an
assembly of many individual tiles, assembled into a structure to
provide a combined array. Preferably, the transducer array 14
includes between about two hundred and ten thousand (200-10,000)
transducer elements 22. The transducer elements 22 may have a
width, diameter, or other maximum cross-sectional dimension across
their surface area that is on the order of the wavelength of the
acoustic energy that is transmitted by the transducer elements 22.
For example, the transducer elements 22 may have a cross-sectional
dimension between about 0.8 and seven millimeters (0.8-7 mm), which
are on the order of the wavelength of ultrasonic energy between
about two and 0.2 Megahertz (2-0.2 MHz), respectively. The specific
number of transducer elements and their sizes, however, is not
important to the present invention, and the systems and methods
discussed herein may be applicable to a transducer array 14
including a variety of different configurations of transducer
elements 22.
[0029] The driver 16 and/or the controller 18 may be coupled to the
transducer array 14 via the switch 20 for causing the transducer
elements 22 to transmit acoustic energy. Generally, the driver 16
includes an oscillator and/or other component(s) (not shown)
enabling the driver 16 to generate electrical drive signals, which
may be controlled by the controller 18. The driver 16 may generate
drive signals in the ultrasound frequency spectrum that may be as
low as twenty kilohertz (20 kHz), and that typically range from
about 0.3 to three Megahertz (0.3-3.0 MHz). Preferably, the driver
16 provides radio frequency (RF) drive signals, for example,
between about 0.3-3.0 MHz, and more preferably between about
0.5-2.5 MHz. When the drive signals are delivered to the transducer
array 14, the transducer elements 22 convert the electrical drive
signals into vibrational energy, as represented by the acoustic
beam 15. Exemplary drivers and/or controllers that may be used to
generate sets of drive signals are disclosed in U.S. Pat. No.
6,506,154, the disclosure of which is expressly incorporated herein
by reference.
[0030] The driver 16 and/or controller 18 may be separate from or
integral components of the transducer array 14, and/or may be
separate components from or integral with one another. It will be
appreciated by one skilled in the art that the operations performed
by the driver 16 and/or controller 18 may be performed by one or
more controllers, processors, and/or other electronic components,
including software or hardware components.
[0031] As shown in FIG. 1, the driver 16 includes a number "m" of
output channels 34 that provide respective sets of drive signals
(s.sub.1, s.sub.2, s.sub.3, . . . s.sub.m) having respective phase
shift values (.theta..sub.1, .theta..sub.2, .theta..sub.3, . . .
.theta..sub.m). The number "m" of output channels 34 is generally
substantially less than the number "n" of transducer elements 22,
and preferably "m" is orders of magnitude smaller than "n." For
example, "n"/"m" could be between about ten and one hundred
(10-100), or even more than one hundred (100).
[0032] The switch 20 generally includes an "m" number of inputs 36,
an "n" number of outputs 38, and a plurality of switches (not
shown) therein. The "m" output channels 34 from the driver 16 may
be coupled to the "m" inputs 36 of the switch 20, respectively, and
the "n" outputs 38 of the switch 20 may be coupled to the "n"
transducer elements 22, respectively. Thus, the switch 20 may allow
respective inputs 36 to be selectively connected to one or more
respective outputs 38, thereby delivering sets of drive signals
with different phase shift values to respective transducer elements
22.
[0033] The switch 20 may be a cross-point matrix, a multistage
interconnection network ("MIN"), or other switching device enabling
multiple inputs to be selectively connected to one or more
respective outputs, as is known in the art. Preferably, the switch
20 is mounted to the transducer array 14, e.g., to the substrate 24
opposite the transducer elements 22, as shown in FIG. 2. Wires,
cables, conductive paths, or other conductors (generally referred
to herein as "leads," not shown) may extend between the outputs 38
of the switch 20 and respective transducer elements 22, e.g., along
the substrate 24 or otherwise contained within the transducer array
14. The leads should electrical connectivity, while mechanically
isolating the transducer vibrating elements from the substrate 24.
Alternatively, the switch 20 may be mounted in close proximity to
the transducer array 14, i.e., not directly mounted to the
substrate 24.
[0034] Wires or other leads, e.g., within one or more cables (also
not shown), may extend from the inputs 36 of the switch 20 to the
driver 16. This arrangement may substantially simplify wiring of
the transducer array 14, since only "m" leads are required for the
cable(s) connecting the transducer array 14 to the driver 16,
rather than "n" leads, as would be required if each transducer
element 22 were separately connected to the driver 16.
[0035] If the system 10 is used in conjunction with magnetic
resonance imaging ("MRI"), parts of the switch 20, including any
leads should be made from nonmagnetic materials, as is well known
to those skilled in the art optionally, the leads may include one
or more connectors (not shown) for detachably connecting them to
any of the components described herein, as is known in the art.
[0036] The controller 18 may control the driver 16, e.g., to
control one or more characteristics of the drive signals generated
by the driver 16. For example, the controller 18 may control an
amplitude of the drive signals, and, consequently, the intensity or
power of the acoustic waves transmitted by the transducer 14, as is
known in the art, and/or the phase allocation to each of the "m"
leads 34 leaving the driver 16.
[0037] In addition, the controller 18 may also control and/or
assign phase shift values to the drive signals in order to steer
and/or focus the acoustic energy in a desired manner. For example,
the controller 18 may divide a full cycle (360.degree. or 2.pi.
radians) by the number of output channels 34 of the driver 16 and
assign sequential phase shift values, e.g., between 0.degree. and
360.degree. to the sets of drive signals. Thus, for a driver
including ten (10) output channels, the phase shift values assigned
to the sets of drive signals and output channels could be as
follows: s.sub.1: .theta..sub.1=36.degree., s.sub.2:
.theta..sub.2=72.degree.0, s.sub.3: .theta..sub.3=108.degree., . .
. s.sub.10: .theta..sub.10=360.degree.. It will be appreciated that
the controller 18 may assign phase shift values using other
methodologies, and cause the driver 16 to generate sets of drive
signals based upon the assigned phase shift values.
[0038] Further, the controller 18 may be configured to generate one
or more tables relating sets of drive signals to the transducer
elements 22 that may be used by the system 10. The controller 18
may include one or more processors (not shown) for generating the
data for the tables, and/or memory (also not shown) for storing the
one or more tables.
[0039] For example, the controller 18 may generate respective
desired phase shift values for the transducer elements 22 based
upon parameters for a particular treatment, and create a first
table of desired phase shift values for the transducer elements 22.
The data in the first table may be based upon a desired focal
depth, a desired focal zone shape, compensation for tissue
aberrations encountered during a particular treatment, compensation
for variances in the relative impedance of the transducer elements,
and/or compensation for geometric inaccuracies in positioning the
transducer elements 22 relative to one another on the transducer
array 14. A hypothetical set of desired phase shift values for a
transducer array including "n" elements is shown in FIG. 3A.
[0040] Alternatively, it will be appreciated that separate tables
may be generated for one or more of these parameters, e.g., for
different beam paths, focal zone locations, and/or focal depths.
During a procedure, one or more sets of tables may be loaded, e.g.,
to reconfigure the switch 20 during a procedure. This may provide
the controller 18 with even greater flexibility to switch steering
and focusing dynamically.
[0041] First, the controller 18 may assign phase shift values to
each of the transducer elements 22 based upon a desired location
for the focal zone 17 of the transducer array 14. For example, the
controller 18 may assign phase shift values to transducer elements
22 based upon their circumferential location around the central
axis "z" and/or their radial distance from the central axis "z."
These phase shift values may change the size and/or shape of the
resulting focal zone 17, and/or may adjust the focal depth, as is
known in the art. In addition, the controller 18 may assign phase
shift values to the transducer elements 22 that move the focal zone
laterally relative to the central axis "z," i.e., to steer the
focal zone away from the central axis "z," and/or to generate
multiple focal zones simultaneously. Exemplary systems and methods
for achieving such steering are disclosed in co-pending application
Ser. No. 09/724,611, filed Nov. 28, 2000. The disclosures of this
reference and any others cited therein are expressly incorporated
herein by reference.
[0042] Second, the controller 18 may compensate for tissue
aberrations, i.e., phase shifts that may occur due to the acoustic
energy from respective transducer elements 22 traveling along
different acoustic paths having different densities, e.g., when the
acoustic energy passes through different tissue structures. The
controller 18 may analyze an acoustic path from each of the
transducer elements 22 through intervening tissue structures to the
target region 92, e.g., using magnetic resonance imaging,
ultrasound imaging, and the like. Exemplary systems and methods for
compensating for tissue aberrations are disclosed in application
Ser. Nos. 09/724,817, filed Nov. 28, 2000, and Ser. No. 10/190,787,
filed Jul. 8, 2002, the disclosures of which are expressly
incorporated herein by reference. The phase shift values for
compensating for tissue aberrations may be added to any other phase
shift values assigned by the controller 18, e.g., those desired to
control the size and/or location of the resulting focal zone, to
provide phase corrections correcting for physical tolerances in the
transducer structure, and/or to compensate for impedance variations
between the different elements, as is known in the art.
[0043] Once the desired phase shift values for the transducer
elements 22 are known, the controller 18 may assign sets of drive
signals to the transducer elements 22 to create a second table of
assigned drive signal-transducer element relationships. For
example, the controller 18 may compare the phase shift values of
the sets of drive signals to the desired phase shift values for the
transducer elements 22, and assign each of the transducer elements
22 to a set of drive signals that has a phase shift value that
approximates the desired phase shift value for the respective
transducer element. The controller 18 may round the desired phase
shift value for each of the transducer elements 22 off to the
nearest phase shift value corresponding to one of the sets of drive
signals.
[0044] For example, using the exemplary ten phase shift values and
associated sets of drive signals discussed above, if the desired
phase shift value of a given transducer element was 30.degree., the
transducer element would be assigned to s.sub.1:
.theta..sub.1=36.degree., while a transducer with a desired phase
shift value of 84.degree. would be assigned to s.sub.2:
.theta..sub.2=72.degree.. Alternatively, the desired phase shift
values could be truncated or associated with respective sets of
drive signals using other methodologies. An exemplary table showing
transducer elements assigned to respective output channels, and
consequently, respective phase shift values is shown in FIG.
3B.
[0045] Once each of the transducer elements 22 has been assigned to
a respective set of drive signals, the controller 18 may generate a
third table to control the switch 20, e.g., based upon the drive
signal-transducer element assignments in the second table. For
example, if the switch 20 is a cross-point matrix, the third table
may instruct the cross-point matrix to configure its switches in a
particular manner to connect the inputs 36 to respective outputs 38
in order to connect the transducer elements 22 to the output
channels 34 corresponding to their assigned sets of drive signals.
The controller 18 may control the switch 20 directly, or the switch
20 may include its own controller (not shown). An exemplary table
identifying inputs and outputs of a switch to connect to one
another is shown in FIG. 3B, based upon the data from FIGS. 3A and
3B discussed above. optionally, the controller 18 may also control
a physical position or orientation of the transducer array 14. For
example, as shown in FIG. 2, the system 10 may include a mechanical
positioner 48 connected to the transducer array 14 that may move
the transducer array 14 in one or more dimensions, and preferably
in any of three orthogonal directions. Exemplary transducers and
positioning systems are disclosed in co-pending applications Ser.
Nos. 09/556,095 and 09/557,078, both filed Apr. 21, 2000, and Ser.
No. 09/628,964, filed Jul. 31, 2000. The disclosures of these
references and any others cited therein are expressly incorporated
herein by reference. Thus, the transducer array 14 may be focused
electronically, mechanically, or using a combination of the two,
and/or the focus zone may be moved within the target 92
electronically, mechanically, or using a combination of the
two.
[0046] As shown in FIG. 2, the transducer array 14 may be mounted
within a casing or chamber 40 filled with degassed water or similar
acoustically propagating fluid. The chamber 40 may be located
within a table 42 upon which a patient 90 may be disposed, or
within a fluid-filled bag mounted on a movable arm that may be
placed against a patient's body (not shown). The top of the table
42 generally includes a flexible membrane 44 that is substantially
transparent to ultrasound, such as mylar, polyvinyl chloride (PVC),
or other suitable plastic material. A fluid-filled bag 46 may be
provided on the membrane 44 that may conform easily to the contours
of the patient 90 disposed on the table 42, thereby acoustically
coupling the patient 90 to the transducer array 14 within the
chamber 40. In addition or alternatively, acoustic gel, water, or
other fluid (not shown) may be provided between the patient 90 and
the membrane 44 to facilitate further acoustic coupling between the
transducer array 14 and the patient 90, as is known to those
skilled in the art.
[0047] In addition, the system 10 may include an imaging device
(not shown) for monitoring the use of the system during treatment
of a patient. For example, the system 10 may be placed within a
magnetic resonance imaging (MRI) system, such as that disclosed in
U.S. Pat. Nos. 5,247,935, 5,291,890, 5,368,031, 5,368,032,
5,443,068 issued to Cline et al., and U.S. Pat. Nos. 5,307,812,
5,323,779, 5,327,884 issued to Hardy et al., the disclosures of
which are expressly incorporated herein by reference.
Alternatively, an acoustic imaging device may be provided, or the
transducer array 14 itself may be used for imaging, as is known to
those skilled in the art.
[0048] Returning to FIG. 2, during use, a patient 90 may be
disposed on the table 42 with water, ultrasonic conducting gel, and
the like (not shown) applied between the patient 90 and the bag 46
or membrane 44, thereby acoustically coupling the patient 90 with
the transducer array 14. The transducer array 14 may be oriented
generally towards a target tissue region 92, e.g. within a tissue
structure, such as a cancerous or benign tumor within an organ,
e.g., a liver, kidney, pancreas, uterus, brain, and the like.
[0049] The acoustic path from the transducer array 14 to the target
tissue region 92 may be analyzed, e.g., using MRI or ultrasound
imaging, as explained above. For example, the acoustic path from
each of the transducer elements 22 to the target tissue region 92
may be analyzed to determine tissue types or other characteristics
that may affect the speed of the acoustic energy passing through
intervening tissue between the transducer elements 22 and the
target tissue region 92. Phase shift values may be determined for
each of the transducer elements 22 to compensate for these
variations in speed in order to maintain the focus of the acoustic
energy substantially at the desired focal zone 17.
[0050] Optionally, if the analysis discovers that there are
obstructions or high sensitivity volumes along an energy pass zone
through which it is desired to prevent acoustic energy from passing
(e.g., air-filled cavities, non-targeted thick bone, and the like),
individual transducer elements 22 may be deactivated (e.g., have
their amplitude set to zero (0)) in order to prevent acoustic
energy from being transmitted by the relevant transducer elements
22.
[0051] Once any acoustic path analysis is complete, the controller
18 may be instructed to generate a treatment procedure, which may
involve a single or multiple "sonications" (i.e., finite time
periods during which the transducer array 14 is activated to
deliver acoustic energy to a focal zone at a particular location
within the target tissue region 92). The controller 18 and/or the
operator may set the number and duration of sonications to be used
to treat the target tissue region 92. The controller 18 may
generate the tables described above and/or otherwise instruct the
switch 20 in order to connect the output channels 34 of the driver
16 to respective transducer elements 22.
[0052] First, the controller 18 may assign phase shift values to
the sets of drive signals that will be provided at each of the
output channels 34 of the driver 16. Alternatively, the phase shift
values of the sets of drive signals may be fixed, e.g., based upon
phase errors required to achieve a predefined focus quality. For
example, continuous wave (CW) acoustic beam forming in phased
arrays requires the ability to control phase errors between
different transducer elements to a particular level, e.g., better
than .lambda./10, where .lambda. is the wavelength of the acoustic
energy defining the acoustic beam. Because phase corrections are
modulo 2.pi., it would be desired to have phase accuracy better
than 2.pi./10. Given this desired accuracy, it may be able to
attain the desired phase error corrections with as few as ten (10)
phase values. It will be appreciated that more or fewer phase shift
values, and consequently, output channels, may be provided. In an
exemplary embodiment of a transducer array including two thousand
(2,000) transducer elements, thirty two (32) phase values and
output channels may be used.
[0053] The controller 18 may then determine desired phase shift
values for the transducer elements 22 of the transducer array 14,
taking into account focal zone shape, focal depth, steering angle,
equal power distribution between drive channels, and tissue
aberrations, as discussed above. One or more tables may be
generated assigning each of the transducer elements 22 to one of
the output channels 34, and the switch 20 may be set to connect the
transducer elements 22 to the driver 16 based upon the generated
tables.
[0054] Once the switch 20 is properly configured, the driver 16 may
be activated in order to provide respective sets of drive signals
to the transducer array 14. As explained above, the transducer
elements 22 transform the drive signals into acoustic energy,
represented by energy beam 15. As the acoustic energy 15 passes
through the patient's body, the acoustic energy 15 is converted to
heat at the focal zone 17, thereby raising the temperature of
tissue within focal zone 17. The acoustic energy may be focused for
sufficient time to raise the temperature of tissue within the focal
zone 17 to necrose the tissue, while minimizing damage to
surrounding tissue.
[0055] For example, the transducer array 14 may be activated for
about ten seconds or more, e.g., between about two and forty (2-40)
seconds, and preferably between about four and twenty seconds. Once
a sonication is completed, the transducer array 14 may be
deactivated, for example, for sufficient time to allow heat
absorbed by the patient's tissue to dissipate, e.g., for about
sixty (60) seconds. The transducer array 14 may then be focused at
another focal zone within the target tissue region 92, for example,
adjacent to the previous focal zone 17, and the process repeated
until the entire target tissue region 92 is ablated.
[0056] Thus, during each sonication, the output channels 34 of the
driver 16 may be connected to multiple transducer elements 22. This
may substantially reduce the number of output channels 34 required
for the transducer array 14, thereby substantially simplifying
connection between the driver 16 and the transducer array 14.
Preferably, the system 10 allows substantially more and smaller
transducer elements to be provided for a given transducer array
size and configuration, thereby enhancing the ability to steer the
acoustic energy and focus the acoustic energy more precisely than
conventional systems. Thus, it may be possible to steer the
transducer array 14 to control the focal zone entirely using
electronic steering, thereby eliminating the need for mechanical
positioning systems and/or allowing simpler transducer
configurations (e.g., planar arrays) to be used.
[0057] Although the systems and methods described herein have
described ablating or otherwise treating tissue, the systems and
methods of the present invention may also be used to perform other
therapeutic or diagnostic procedures, e.g., ultrasound imaging and
the like.
[0058] While the invention is susceptible to various modifications,
and alternative forms, specific examples thereof have been shown in
the drawings and are herein described in detail. It should be
understood, however, that the invention is not to be limited to the
particular forms or methods disclosed, but to the contrary, the
invention is to cover all modifications, equivalents and
alternatives falling within the scope of the appended claims.
* * * * *